Electroconductive coated paper and method for preparing same



United States Patent U.S. Cl. 117201 16 Claims ABSTRACT OF THE DISCLOSURE There is provided an electrically conductive paper adapted for non-impact printing containing on its surface a continuous coating of an electroconductive azine complex having at 20 C. a resistivity lower than about 5 X ohms-cm. and conforming to the configuration:

l lml ln wherein D is an azine selected from the group consisting of a phenothiazine and a phenoselenazine, A represents a dihalogen dicyano-p-benzoquinone, m and n are each an integer from 1 to 3, said complex being present in amounts corresponding to from about 10 milligrams to about 100 milligrams of the complex per square foot of the paper.

The present invention relates to electroconductive coated paper and to a method for preparing the same. More particularly, it relates to electroconductive coated paper adapted for use in direct-type electrographic printing independent of ambient humidity conditions. Still more particularly, it relates to the manufacture of paper having a printing surface containing an electroconductive substance consisting of a hereinbelow defined azine complex, eminently suited for direct-type electrographic or non-impact printing.

In the Electrofax process for photocopying information, it is known that the photosensitive paper plays a dominant role in the success or failure of this process. Usually, an ordinary sheet of paper, to be rendered photosensitive, is initially treated with a conducting substance to lower the papers resistance to lower than 10 ohms/square. The paper is next top-coated with a photoconductive substance which has a resistance substantially higher than about 10 ohms/square. Next, the paper is given an electrostatice charge using a corona discharge device. An image is then formed by passing the paper in front of a video tube. The light which strikes the photoconductive surface allows the static charge to dissipate in the light-struck areas. The charge is carried off by the low-resistance substances present in the paper, leaving an electrostaic image on the photoconductive layer. Finally, powdered pigment resin is dusted on the surface of the latter layer. With sufficient heat applied, fusion occurs and a permanent image is formed. However, in this system, there exists a distinct need for a conductive base paper, for otherwise designated electrostatic charges cannot be removed from the paper after exposure to light. Unfortunately, the electrical conductivity of untreated paper is very low, especially when the paper is dry. To improve conductivity, it has been proposed to top coat paper with an aqueous solution of an inorganic salt. However, salt-type electrolytes lose their effectiveness at humidities lower than about 50% RH. To lessen or eliminate the role of humidity on conductivity, it has been further proposed to add carbon black particles, metallic particles or even metallic foil to base paper.

3,440,090 Patented Apr. 22, 1969 To the present, each of the known conductive substances suffers from at least one major serious drawback. While metallic or carbon substances do not rely upon humidity to lessen electrical resistance in paper, the fact is that the incorporation of the latter into normally white paper is not wholly acceptable. Such procedure necessarily causes discoloration. Additionally, paper to which a metallic foil is laminated loses its normal feel and tends to curl in the hands of the user. Thus, there remains a long-felt need for electrically conductive paper which can be employed under conditions substantially independent of relative humidity and being substantially free from both curling and unsightly discoloration.

The term resistance, as employed in this specification, is defined as the lateral resistance between two parallel bar-shaped electrodes pressed against the surface of the paper. The distance between the bars is adjusted so that their distance and length are equal to each other. Thus, the resistance is expressed as ohms per square.

In the present practice, it has been unexpectedly found that the normally high resistance of any cellulosic material, such as ordinary paper, particularly at low relative humidities usually from about 0% to about 50%, can substantially be reduced to provide an expectedly high electroconductive surface. This is accomplished by utilizing azine complexes inherently possessing a resistivity at 20 C. of less than about 5x10 ohms-cm. of the type:

where D is an azine, such as a phenothiazine or a phenoselenazine, A is a dihalogenodicyano-p-benzoquinone and m and n are each an integer from 1 to 3 which may be the same or different. Such complexes are incorporated in or coated on a cellulosic or paper material to render its surface electroconductive by reducing its resistance from about 10 ohms per square to about 10 ohms, or less, per square over a wide range of relative humidity (R.H.) conditions, ranging from about zero percent (0%) to about fifty percent (50%), or higher. In general, from about ten (10) milligrams to about one hundred milligrams of the azine complex per square foot of surface are incorporated in or coated on the cellulosic material.

Advantageously, the azine complexes can be prepared in a straightforward manner by reacting a dihalodicyano p-benzoquinone, such as dichlorodicyano-p-benzoquinone or dibromodicyano-p-benzoquinone with exemplary benzo[c,d]phenothiazine or dibenzo[c,d]phenoselenazine to form an azine complex inherently possessing relatively low electrical resistivities of less than about 5x10 ohmscm. The color of the resultant azine complex ranges from dark green to black. Nonetheless, darkening of ordinarily white paper is insignificant since the amount of complex employed is relatively miniscule. Moreover, a cellulosic substrate treated in accordance with the process of the invention has a good hand feel.

Any cellulosic substrate, such as paper whether sized or unsized, can be treated with a solution of an azine complex. In one procedure, the azine complex may be formed stepwise by coating a substrate with an exemplary dibenzo [c,d] phenothiazine or dibenzo [c,d] phenoselenazine in an inert solvent, evaporating the solvent and then applying a second solution of a dihalodicyano-p-benzoquinone to the so-treated substrate. The order of steps in applying the reactants to form the azine complex does not appear to be critical. Another procedure involves the incorporation or coating of a substrate with a solution of a preformed azine complex in an inert solvent. The latter is a preferred embodiment since the complexs resistivity can be determined prior to its use on the cellulosic substrate.

In general, the inert organic solvents contemplated for both the reactants per se and the complex as formed are aliphatic as well as aromatic solvents. These include acetone, benzene, toluene and dimethylsulfone, as exemplary.

Commercially-available cellulosic materials, such as paper, may be employed. These include, for instance, a rosin-sized bond paper, a ketone dimer-sized bond paper, a kraft saturating paper and a groundwood (Mimeograph) paper. Ordinarily, where a sized paper is not employed, the quantity of azine complex added is increased to approach the upper stated limit, since the cellulosic web adsorbs a portion of the azine complex prior to forming a continuous surface film. Lesser quantities of the complex can be tolerated when utilizing sized substrate. Thus, the latters use is a preferred practice.

As stated hereinabove, the preparation of the substrate is accomplished either batchwise or continuously by methods known in the art. For instance, a solution of the complex can coat, as b brushing or spraying the substrate or by dipping, the substrate into the azine complex solution. Alternatively, the complex may be added to paper pulp prior to the making of the paper, resulting in a paper of substantially reduced resistivity.

In general, the amount of the azine complex can be widely varied. Usually, the addition of from 10 milligrams (i.e., 1 10- ounce) to 100 milligrams (i.e., 1 10- Ounce) of the complex per square foot of the paper is a good practice. Resultant highly electrically-conductive paper is finally coated with a photoconducting insulator. One such widely used substance is zinc oxide. The paper is now ready for use in the Electrofax photocopying process.

In the following examples there are presented illustrative but non-limitative procedures to more fully describe the practice of the invention. Unless otherwise stated, the

parts and percentages given are by weight.

The preparation of azine complexes is illustrated in Examples A through F hereinbelow. In determining the resistivity of the exemplified complexes, a four probe method is employed. In this procedure, the test complex is compressed to a three-eighths inch diameter and mounted on a resistivity test device (Model B manufactured by A & M Fell, Ltd., England). The resistivity is read directly from an ohmmeter, such as a Keithly (Model 502) milliohmmeter.

EXAMPLE A l o I s NC On analysis of the complex, the following elemental content in percent is recorded:

Theory f! (C20H13NS)2.C3C12N202: C, H, CI, 8.6; S, 7.8. Found: C, 69.8; H, 3.2; CI, 8.7; S, 7.6.

EXAMPLE B In a suitable reaction vessel 0.95 part (3.0 millimoles) of 2,3-dibromo-5,6-dicyano-p-benzoquinone in 50 parts of benzene, by volume) and a hot benzene solution of dibenzo[c,d]phenothiazine containing 0.90 part (3.0 millimoles) of the thiazine in 200 parts of benzene (by volume) are admixed. Resultant mixture is next cooled to room temperature and a black precipitate which forms is filtered, washed with benzene and finally washed with ether. On analysis, it is found that the thiazine complex which possesses a resistivity of 240 ohms-cm. at 20 C. conforms to the configuration:

EXAMPLE C Preparation of the complex:

\s/ NC 068 part (3.0 millimoles) of dichlorodicyano-p-benzoquinone in 1 00 parts (by volume) of benzene is added to a part (by volume) of hot benzene solution of benzo- [c,d]phenothiazine containing 0.75 part (3.0 millimoles) of the thiazine. Resultant composition is cooled to room temperature and the black precipitate formed is filtered, washed with benzene and subsequently with ether.

Analysis of the complex having a resistivity at 20 C. equal to 4x10 ohms-cm. is as follows in percent:

Theory for C1H11NS.C3C12N202Z C, H, CI, 14.9; S, 6.7. Found: C, 61.0; H, 2.7; CI, 15.1; S, 6.7.

EXAMPLE D Preparation of the complex:

I o /N H s No 0.45 part (2.0 millimoles) of dichlorodicyano-p-benzoquinone in 70 parts (by volume) of benzene is added to a 200 parts by volume of hot benzene solution of dibenzo- [c,d]phenothiazine containing .90 part (3.0 millimoles) of the thiazine. The precipitate formed is filtered, washed with benzene and subsequently washed with ether.

Analysis of the complex having a resistivity at 20 C. equal to 5x10 ohms-cm. is as follows in percent:

Theory for C20H13NS.C8Ci2N202: C, H, Ci, 13.5; S, 6.1. Found: C, 63.9; H, 2.6; CI, 12.9; S, 6.4.

EXAMPLE E Preparation of the complex:

Se NC .45 part 2 millimoles) of dichlorodicyano-p-benzoquinone in 50 parts (by volume) of benzene is added to a 220 parts (by volume) of hot benzene solution of dibenzo[c,d]phenoselenazine containing 1.38 parts (4 millimoles) of the selenazine. The solution is cooled to room temperature and a black precipitate formed is filtered and washed with benzene.

Analysis of the complex having a resistivity of 6 10 ohms/ cm. is as follows in percent:

Theory for C H NSe.C Cl N O C, H, N, 7.3; Cl, 12.4. Found: C, 58.9; H, 2.6; N, 7.1; Cl, 12.2.

EXAMPLE F Preparation of the complex:

s IS

0.32 part (1 millimole) of dibromodicyano p benzoquinone in parts (by volume) of benzene is added to a parts (by volume) of hot benzene solution of phenothiazine containing 0.20 part (1 millimole) of the thiazine. The mixture is cooled to room temperature and a black precipitate formed is filtered and wished with benzene and subsequently with ether.

Analysis of the product having a resistivity at 20 C. of 2x10 ohms-cm. is as follows in percent:

Theory for c,,H,Ns.c,Br,N,o,: C, 46.6; H, 1.8; S, 6.2; Br, 31.1. Found: C, 47.1; H, 2.0; S, 6.2-, Br, 31.3.

Although benzene is employed in the above examples as a mutual solvent for the reactants, any inert solvent, such as, for instance, acetone, toluene or dimethylsulfone may be substituted for the benzene employed above.

EXAMPLE 1 A sheet of 50 pounds per ream of bleached sulfite base paper, sized on one side, is sprayed on the sized side with a benzene solution containing 0.1% by weight of the solution of the thiazine complex prepared in accordance with Example A above. The paper so sprayed is dried in an oven to remove solvent therefrom and weighed. The paper contains a coating equivalent to 10 milligrams per square foot of the paper. Test pieces cut from the coated paper indicate that the conductivity is increased by noting that the resistivity of the coated paper at 0% RH. (i.e., relative humidity) is higher than 10 ohms/ square R.H. whereas the coated paper exhibits a resistivity at 0% RH. of 3x10 ohms per square. When increasing the relative humidity to 40%, the resistance of the so-treated paper decreased to 1X 10 ohms per square. Since the electrical resistance of the paper from 10 to 10 ohms per square is decreased, the electrical conductance under the same condition-s has been correspondingly.increased.

EXAMPLE 2 Repeating the procedure of Example 1 in every detail except that the bleached sulfite paper base is sized on both sides and dipped into a benzene solution containing 0.1% by weight of phenothiazine complex as prepared in Example B above. At 0% R.H., the uncoated or complex-treated paper exhibits a resistance equal to 10 ohms per square, whereas the coated paper exhibits a resistivity at 0% RH. of 3x10 ohms per square and at 40% RH. the resistance of the coated paper decreases to 1x10 ohms per square.

Advantageously, the above results can be obtained when a solution of the complex is incorporated into the pulp prior to the formation of paper by increasing the quantity of the complex by a factor of from about 5 to 10.

EXAMPLE 3 Following the procedure of Example 1 in every detail except that the bleached sulfite paper base is sized on both sides and dipped into a solution containing 1.0% by weight of phenoselenazine complex as prepared in Example E above. The uncoated paper at 0% relative humidity exhibits a resistance equal to 10 ohms per square, whereas the coated paper exhibits at 0% RH. a resistivity of 2x10 ohms per square.

Substituting the complex prepared in Example C or D above in lieu of the complex of Example 3, substantially the same low resistivity attaches to the treated paper at 0% RH.

I Claim:

1. An electrically conductive paper adapted for nonimpact printing containing on its surface a continuous coating of an electroconductive azine complex having at 20 C. a resistivity lower than about 5x10 ohms-cm. and conforming to the configuration:

s NC 3. A paper according to claim 1 in which the complex is defined by the structure:

4. A paper according to claim 1 in which the complex is defined by the structure:

l o N n C l P-Cl s NC 01 5. A paper according to claim 1 in which the complex is defined by the structure;

S NC

6. A paper according to claim 1 in which the complex is defined by the structure:

7. A paper according to claim 1 in which the complex is defined by the structure:

NC I Br a resistivity lower than about 5x10 ohms-cm. and having the formula:

NC Br wherein D is an azine selected from the group consisting of a phenothiazine and a phenoselenazine, A represents a dihalogen dicyano-p-benzoquinone, m and n are each an integer from 1 to 3, said complex being present in amounts corresponding to from about milligrams to about 100 milligrams of the complex per square foot of the paper, and a top finishing coating comprising a photoconducting layer.

9. The paper according to claim 8 wherein the top photoconducting layer is zinc oxide.

10. A method for preparing a highly electrically conductive paper eminently adapted for non-impact printing which comprises the steps of: sizing at least one side of an unprinted paper and coating the said paper with a solution of an azine complex in an inert solvent, said complex having a resistivity lower than about 5x10 ohms-cm. and having the formula:

wherein D is an azine selected from the group consisting of a phenothiazine and a phenoselenazine, A represents a dihalogen dicyano-p-benzoquinone, m and n are each an integer from 1 to 3, said complex being present in amounts corresponding to from about 10 milligrams to about 100 milligrams of the complex per square foot of the paper.

11. A method according to claim 10 in which the azine complex is:

s NC

8 12. A method according to claim 10 in which the azine complex is:

I o N I NC Br s NC Br 13. A method according to claim 10 in which the azine complex is:

| o N l U l o i 14. A method according to claim 10 in which the azine complex is:

15. A method according to claim 10 in which the azine complex is:

86 NC I 16. A method according to claim 10 in which the azine complex is:

References Cited UNITED STATES PATENTS 3,118,789 1/ 1964 Wiswellet al.

ALFRED L. LEAVITT, Primary Examiner.

W. F. CYRON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO 3 ,440 ,090 April 22 1969 Yoshio Matsunaga It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 56, "electrostaic" should read electrostatic line 67, "lose" should read loose Column 2, line 8, "loses" should read looses Column 3, line 53, "triazine" should read thiazine Column 4, line 41,

"068" should read O. 68 Column 5 line 16, "220 10 parts" should read 220 parts line 41, "wished" should read washed Column 7, lines 15 to 20, that portion of the formula reading II I should read Se Se Signed and sealed this 21st day of April 1970.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

